Abstract
In this study, a comprehensive investigation on nano-scale machining of polycrystalline copper structures is carried out by molecular dynamics (MD) simulation. Simulation cases are constructed to study the impacts of grain size, as well as various machining parameters. Six polycrystalline copper structures are produced, which have the corresponding equivalent grain sizes of 5.32, 6.70, 8.44, 13.40, 14.75, and 16.88 nm, respectively. Three levels of depth of cut, machining speed, and tool rake angle are also considered. The results show that greater cutting forces are required in nano-scale polycrystalline machining with the increase of depth of cut, machining speed, and the use of the negative tool rake angles. The distributions of equivalent stress are consistent with the cutting force trends. Moreover, it is discovered that in the grain size range of 5.32 to 14.75 nm, the cutting forces and equivalent stress increase with the increase of grain size for the nano-structured copper, while the trends reserve after the grain size becomes even higher. This discovery confirms the existence of both the regular Hall–Petch relation and the inverse Hall–Petch relation in polycrystalline machining, and the existence of a threshold grain size allows one of the two relations to become dominant. The dislocation-grain boundary interaction shows that the resistance of the grain boundary to dislocation movement is the fundamental mechanism of the Hall–Petch relation, while grain boundary diffusion and movement is the reason of the inverse Hall–Petch relation.
Highlights
Built on the classical Newton's Second Law, molecular dynamics (MD) simulation has been proven to be an effective tool to study many underlying intriguing mechanisms of material processing
Other phenomena in nano-scale machining are investigated by MD simulation approach
This paper represents an extensive study of using MD simulation approach to investigate machining of polycrystalline structures at nano-scale
Summary
Built on the classical Newton's Second Law, molecular dynamics (MD) simulation has been proven to be an effective tool to study many underlying intriguing mechanisms of material processing. Fang and Weng [4] simulated nano-scale machining of monocrystal copper using a diamond tool by focusing on friction. Promyoo et al [10] investigated the effects of tool rake angle and depth of cut in nano-scale machining of monocrystal copper. A numerical study of surface residual stress distribution of silicon during nano-machining process is presented by Wang et al [16] Their MD simulation results revealed that higher hydrostatic pressure beneath the tool rake face induces more drastic phase transformation and generates more compressive surface residual stress. Ji et al [17] studied the tool-chip stress distribution in nano-machining of copper, and the results were compared to the existing models of conventional machining. It was used to establish the shape function of the FEM-MD combined model
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